The overall objective of the research program is to delineate basic biological mechanisms underlying the regulation of behavior and neuroendocrine functions in mammals. Three research projects are described in detail. The first project examines the role of the endocrine system in regulating maternal behavior in female rats, while a second project evaluates the role of endogenous opioids in regulating the onset and maintenance of parental care. Using a combination of classical endocrine, molecular, and behavioral approaches, the involvements of lactogenic hormones, endogenous opioids, and molecules secreted by the conceptus in preparing the newly parturient female to respond maternally of her newborns are investigated. The results of these studies will provide a basis for evaluating the effects of endocrine and neurochemical imbalances on mother-young interactions. The third project explores the impact of normal, reproductive experience on subsequent endocrine regulation and neural functioning. Specifically, the effects of prior parity on prolactin secretion and its regulation (dopaminergic, opioidergic, sensory) are studied in famale rats. The consequences of reproductive experience in the adult female likely affect a range of biological junctions, including reproductive senescence, immune function, and a range of behaviors regulated by these neurochemical and endocrine system.